Data center facilities are often used by providers to deliver Internet services to users. A data center, such as a server farm, typically contains thousands of server processing devices. Within the data centers the processing devices are arranged in racks, and each rack may contain dozens of servers. Assuming the power required for a single rack may be in the order of 50 kW, and that there may be hundreds of racks in a data center, it is not uncommon for a data center to have a power requirement on the order of megawatts.
A data center typically receives three-phase power from a utility provider. The three-phase power is provided to each rack, and each rack includes AC to DC converters to convert the AC input to DC output. An example rack receives three-phase power and includes a rectifier for each phase that converts the single phase input to a DC output. The DC output of each rectifier is then coupled to a common DC power bus in the rack that is used to provide power to the DC server components.
In a three-phase system, it is desirable to balance the load on each phase. In general, a perfectly balanced load on the three-phase supply will result in no neutral current. In practice, however, there are always slight imbalances when a load is distributed evenly across the phases. In a data center, for example, such imbalances may arise when servers go down and thus do not require power; when AC to DC converter characteristics drift due to temperature variances or manufacturing variances; and when the phase voltages provided by the utility provider sag. Such imbalances, if sufficiently large, may lead to nuisance breaker trips, power capping, and over/under voltage/current conditions.